In the field of silver halide photographic light-sensitive materials, due to their greater fastness silver images are better suited for recording information required to be permanent than color images (dye images). However, even silver images tend to deteriorate with time. This tendency is aggravated when water-impermeable supports such as plastic films are used as supports. Water-impermeable supports such as platic films are generally better suited for long periods of storage due to their strength, which is higher than that of water-permeable supports such as paper or cloth but, on the other hand, they increase silver image deterioration as described above. Deterioration of silver images on such water-impermeable supports has been reported in Photographic Science and Engineering, Vol. 7, pp. 253-261 (1963), British Patent Application (published unexamined) No. 2,019,024A.
Techniques for preventing deterioration of silver images are disclosed in Japanese Patent Application (OPI) No. 14836/82 (British Patent Application (published unexamined) No. 2,080,963A), which use mercaptobenzimidazole compounds and mercaptotetraazaindene compounds (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
However, the compounds described in the above-described Japanese patent application have the disadvantages that they seriously reduce the sensitivity of the photographic material or result in serious image-blackening by side exposure. The term "image-blackening by side exposure (after-exposure)" means that when light-sensitive materials, after imagewise exposure and before development processing, are exposed, for example, to light from a safelight transmitted through a faded filter (e.g., a filter having been used for one year or more), they are "after exposed" and the entire light-sensitive material appears somewhat blackish after beind developed. The finished images have decreased contrast and an inferior overall impression, and the photographic materials have greatly diminished value as photographic light-sensitive materials.